This invention relates to a method for producing very small diameter metal wire from molten material, of the type in which the wire is obtained by exerting a suitable traction on the end of a glass tube which is adjusted to a viscosity suitable for simultaneous stretching with the metal which is disposed in its interior in the form of wire, powder etc. in the molten state.
Methods of this type are known to comprise at least one heating stage for heating, in a first determined position, a glass tube in which a wire of metal material is disposed, these being fed in the direction of their longitudinal axis in order to continuously give rise to softening of the glass to a required viscosity, and melting of the metal material in order to form a wire, and a cooling stage for cooling, in a second predetermined position, said wire on which a required traction force is exerted.
In this manner, as a result of the softening of the glass to the required viscosity and the melting of the metal material, the cross-section of the wire which forms from this gradually reduces due to the combined action of the temperature and of said traction force, until a wire is obtained having a diameter of the order of a thousandth of a millimeter or even less, and coated with a thin layer of glass.
Said heating stage is normally carried out by electroinduction and said cooling stage by the use of a suitable cooling fluid brought into contact with the wire under formation.
The described known methods have certain serious drawbacks. They cannot be carried out continuously because of the irregularities and frequent breakages which are produced in the wire under formation. In addition, the cooling rate of the wire is rather low and less than that required to obtain wires in the so-called "vitreous" state, i.e. with a substantially amphorous structure, from which favourable wire characteristics derive, as is known. Again, the temperature distribution along the axis of the glass tube and of the metal wire disposed in it, as obtainable by electroinduction heating, is not suitable for producing a uniform continuous wire formation. Finally the speed of formation of the wire is fairly low, and thus taking account of the high plant and operating costs necessary for carrying out the aforesaid methods, these are of little economical convenience.